Storage control apparatus, storage system, and control method for storage system

ABSTRACT

In a storage control apparatus employed in a storage system arranged by containing a plurality of storage control apparatus connected via an IP (Internet Protocol) network to each other, the storage control apparatus stores thereinto necessary storage expiration equal to such an expiration during which data is required to be stored under safe condition, this data being stored in a first storage area of the storage control apparatus; stores thereinto first guarantee expiration equal to such an expiration during which the first storage area can store the data under normal condition; and stores thereinto second guarantee expiration equal to such an expiration during which a second storage area can store the data under normal condition, this second storage area being equal to a storage area of another storage control apparatus. When the necessary storage expiration of the first storage area is expired after the first guarantee expiration of this first storage area, the storage control apparatus transfers the data stored in the first storage area to the second storage area having the second guarantee expiration expired after the first guarantee expiration.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application relates to and claims priority from Japanese PatentApplication No. 2003-401417, filed on Dec. 1, 2003, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a storage control apparatus, astorage system, and a control method for controlling the storage system.

2. Description of the Related Art

In connection with development in IT (Information Technology)industries, storage control apparatus have been rapidly popularized,among which disk array apparatus are typically known. Storage controlapparatus have been firmly utilized as major infrastructure in order torealize storage system employed in information service centers, datacenters and the like in enterprises. In current storage product markets,specific attentions have been paid to virtualization of storage systems.That is, while a plurality of storage control apparatus are connectedvia a network to each other under communicatable condition, since theentire storage system is managed in a unification manner, resources heldin the respective storage control apparatus may be effectively used (seeJP-A-2002-288105).

On the other hand, among data which are managed in storage systems,there are such data which are required to be stored during apredetermined term due to natures of these data. For instance, data ofaccount books in accounting systems and clinical histories in medialbusiness systems must be stored for predetermined terms due to legalresponsibility. Although there is no such a legal responsibility,preselected data should be stored for a predetermined term because ofrules employed in organization. For example, in customer managingsystems, customer data and sales data must be stored for a long timeduration due to a purpose of history management.

In order to store data which are required for such a long preservation,for example, these data are stored into storage media such as magnetictapes for back-up purposes at proper timing. However, storage media suchas magnetic tapes own the following problems. That is, generallyspeaking, such storage media necessarily require lengthy datareading/writing time, so that rapid data processing operations could notbe realized. Further, in order to read/write data with respect to such astorage media, e.g., magnetic tapes, data reading/writing apparatus arerequired. There is another problem as to managing workloads of such datareading/writing apparatus, and cost matters thereof. Also, since both aplace for storing the storage media and a place for installing datareading/writing apparatus must be secured, there is a further problemthat spaces cannot be effectively utilized.

SUMMARY OF THE INVENTION

The present invention has been made to solve these problems, andtherefore, has an object to provide a storage control apparatus, astorage system, and a control method for controlling the storage system,capable of managing data under safe condition.

To achieve the above-described object, a storage control apparatus,according to a major aspect of the present invention, is featured bysuch a storage control apparatus for reading/writing data with respectto a storage device in response to a data input/output requesttransmitted from an information processing apparatus, which is used in astorage system arranged by containing a plurality of storage controlapparatus which are connected via an IP (Internet Protocol) network toeach other under communicatable condition, comprising: a necessarystorage expiration managing unit for storing thereinto a necessarystorage expiration equal to such an expiration during which data isrequired to be stored under safe condition, the data being stored in afirst storage area corresponding to a storage area of the storage deviceto which the storage control apparatus reads/writes the data; a firstguarantee expiration managing unit for storing thereinto first guaranteeexpiration equal to an expiration during which the first storage areacan store the data under normal condition; a second guarantee expirationmanaging unit for storing thereinto a second guarantee expiration equalto such an expiration during which a second storage area can store thedata under normal condition, the second storage area being equal to astorage area of the storage device to which another storage controlapparatus contained in the storage system reads/writes the data; and adata move managing unit operated in such a manner that when thenecessary storage expiration of the first storage area is expired afterthe first guarantee expiration of the first storage area, the data movemanaging unit selects the second storage area having the secondguarantee expiration expired after the first guarantee expiration withinthe second storage area of said another storage control apparatus, andtransfers the data stored in the first storage area to the selectedsecond storage area.

In accordance with the present invention, it is possible to provide sucha storage control apparatus capable of managing the data under the safecondition, and also possible to provide the storage system and themethod of controlling this storage system.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is madeof a detailed description to be read in conjunction with theaccompanying drawings, in which:

FIG. 1 schematically indicates an arrangement of a storage system 1explained as an embodiment of the present invention;

FIG. 2 is a diagram for showing a hardware structure of an informationprocessing apparatus 20 described as an embodiment of the presentinvention;

FIG. 3 is a diagram for representing a hardware structure of a diskarray apparatus 10 explained as an embodiment of the present invention;

FIG. 4 is a diagram for showing functions of the disk array apparatus 10explained as an embodiment of the present invention;

FIG. 5 is a diagram for indicating a move destination logical unitmanagement table 500 explained as an embodiment of the presentinvention;

FIG. 6 is a diagram for representing a logical unit management table 600explained as an embodiment of the present invention;

FIG. 7A is a flow chart for describing a process operation for updatingthe move destination logical unit management table 500 explained as anembodiment of the present invention;

FIG. 7B is a flow chart for describing an example of a process operationwhich is carried out in accordance with an iSCSI protocol when the owndisk array apparatus 10 explained as an embodiment of the presentinvention acquires a portion of information registered in either thelogical unit management table 600 from another disk array apparatus 10or information registered in the logical unit management table 600;

FIG. 8 is a flow chart for explaining both a process operation forjudging as to whether or not move of data stored in the logical unit isrequired, and another process operation for describing that, as to sucha logical unit into which the data being judged to be moved has beenstored, a logical unit which may constitute a move destination candidateis selected, as explained as an embodiment of the present invention; and

FIG. 9 is a flow chart for explaining a process operation related tomove of data, described as an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to drawings, an embodiment of the present invention willbe described.

FIG. 1 schematically shows an arrangement of a storage system 1 which isexplained as an embodiment of the present invention. This storage system1 is arranged by containing a plurality of disk array apparatus 10(namely, storage control apparatus), and one set, or more sets ofinformation processing apparatus 20. Both the disk array apparatus 10and the information processing apparatus 20 are connected to acommunication network (will be referred to as “IP network 60”hereinafter), and thus, the respective disk array apparatus 10 and theinformation processing apparatus 20 are brought into communicableconditions among them. The IP network 60 employs as a communicationprotocol, the TCP/IP (Transmission Control Protocol/Internet Protocol)(registered trademark) protocol.

Structure of Information Processing Apparatus

The information processing apparatus 20 corresponds to a computer, forinstance, a personal computer, a workstation, a server, a main frame,and the like.

FIG. 2 illustratively indicates a hardware structure of the informationprocessing apparatus 20. The information processing apparatus 20 isarranged by employing a CPU (Central Processing Unit) 21, a memory (ROM,RAM) 22, a hard disk drive 23, a recording medium reading apparatus 24,a network interface 25, an input apparatus 26, and an output apparatus27. The recording medium reading apparatus 24 reads data and a programfrom a recording medium such as a CD-ROM and a DVD-ROM. The inputapparatus 26 corresponds to a keyboard, a mouse, and the like. Theoutput apparatus 24 corresponds to a display, a printer, and the like.The network interface 25 performs a communication between the diskapparatus 10 and other information processing apparatus 20 via the IPnetwork 60 in accordance with the TCP/IP protocol. The disk arrayapparatus 10 functions as a storage used for data which is processed byan application program, and the like, which are executed in theinformation processing apparatus 20. The information processingapparatus 20 transmits a data input/output request by way of a blockdesignation to the disk array apparatus 10.

It should be noted that the disk array apparatus 10 may also function asan NAS (Network Attached Storage) which accepts a data input/outputrequest by way of a file name designation from the informationprocessing apparatus 20 in accordance with such a protocol as NFS(Network File System). In the case that the disk array apparatus 10functions as such an NAS, the above-described data input/output requestcorresponds to the data input/output request by the file namedesignation, and a file name is set to the above-described datainput/output request as such an information used to specify data storedin a storage device. When the present invention is embodied, otherstorage control apparatus such as semiconductor disk apparatus may beemployed instead of the disk array apparatus 10.

Structure of Disk Array Apparatus

The disk array apparatus 10 receives a data input/output request whichis transmitted from the information processing apparatus 20 via the IPnetwork 60. The data input/output request corresponds to, for instance,a request for reading data (data reading request) and a request forwriting data (data writing request). The disk array apparatus 10performs to read and write data with respect to a storage device inresponse to a received data input/output request.

FIG. 3 shows a hardware structure of the disk array apparatus 10. Thedisk array apparatus 10 is equipped with a microprocessor 11, a deviceinterface 12, a memory (RAM, ROM) 13, a cache memory 14, an inputapparatus 15 such as an operation panel, an output apparatus 16 such asa display, a communication interface 17, a hard disk device 18functioning as a storage device, a timer 19 for producing presentday/time, and the like. The hard disk drive 18 may be stored in the samehousing into which other structural elements of the disk array apparatus10 are stored, or may be alternatively stored in another housing whichis different from the first-mentioned housing.

The communication interface 17 receives a data input/output requestwhich is transmitted from the information processing apparatus 20 viathe IP network 60, and notifies the received data input/output requestto the microprocessor 11. The communication interface 17 is arranged bycontaining a communication processor 171, and a data transfer processor172. The communication processor 171 is communicated via the IP network60 with respect to the information processing apparatus 20 and anotherdisk array apparatus 10. The communication processor 171 is communicatedwith another disk array apparatus 10 via the IP network 60 in accordancewith an iSCSI (Internet Small Computer System Interface) protocol (see,for example, RFC (Request for Comments) 3347).

The data transfer processor 172 is realized by employing, for instance,a DMA (Direct Memory Access) processor. The data transfer processor 172performs a data transfer operation in a high efficiency between thecommunication interface 17 and the cache memory 14. In a case that theabove-described data input/output request received from the informationprocessing apparatus 20 corresponds to a data writing request, thecommunication interface 17 receives the write data transmitted from theinformation processing apparatus 20, and then writes this write datainto the cache memory 14. In such a case that the above-described datainput/output request received from the information processing apparatus20 corresponds to a data reading request, the communication interface 17reads the read data which has been written into the cache memory 14, andthen transmits the read data to the information processing apparatus 20.

The microprocessor 11 controls an entire arrangement of the disk arrayapparatus 10 in a unification manner. The microprocessor 11 may realizevarious sorts of functions which are provided by the disk arrayapparatus 10 by executing a program stored in the memory 13. When thecommunication interface 17 writes the write data into the cache memory14, the microprocessor 11 notifies this data writing operation to thedevice interface 12. When the device interface 12 writes the read datainto the cache memory 14, the microprocessor 11 notifies this datawriting operation to the communication interface 17.

Both the memory 13 and the cache memory 14 are constituted by employinga RAM, or the like. The memory 13 is used as a storage place of datasupplied from the microprocessor 11. The cache memory 14 may play a roleof buffering an access speed with respect to the hard disk drive 18, andmay improve a response speed with respect to the information processingapparatus 20.

The device interface 12 is arranged by containing a control processor121 and a data transfer processor 122. The control processor 121controls an entire structure of the device interface 12 related to thedata reading/writing operations with respect to the hard disk drive 18.The device interface 12 may be provided with a function for controllingthe hard disk drive 18 based upon a RAID level, for instance, 0, 1, and5 in the RAID (Redundant Array of Inexpensive Disks) system. In a casethat the device interface 12 receives a command from the communicationinterface 17, the control processor 122 reads and writes data withrespect to the hard disk drive 18 in accordance with the receivedcommand. In a case that the above-described command corresponds to acommand for instructing a data reading operation from the hard diskdrive 18, the device interface 12 reads the data from the hard diskdrive 18 in response to the data reading command, and then, writes theread data into the cache memory 14. In the case that the above-describedcommand corresponds to a command for instructing a data writingoperation with respect to the hard disk drive 18, the device interface12 reads the data which has been written in the cache memory 14, andthen, writes the read data into the hard disk drive 18.

Logical Unit

The information processing apparatus 20 recognizes a storage areaprovided by the disk array apparatus 10, while a logical unit “LU”(Logical Unit) corresponding to a logical storage area is used as aunit. In a case that the operating system installed in the informationprocessing apparatus 20 corresponds to such an operating system of theUNIX (registered trademark), the logical unit is defined incorrespondence with a device file (Device File). In such a case that theoperating system installed in the information processing apparatus 20corresponds to an operating system of the Windows (registeredtrademark), the logical unit is defined in correspondence with a driveletter (drive name, drive identifier). To the respective logical units,logical unit numbers “LUNs” (Logical Unit Numbers) specific to therespective logical units have been applied. An LUN is set to, forexample, a data input/output request transmitted from the informationprocessing apparatus 20 to the disk array apparatus 10, and, theinformation processing apparatus 20 designates the LUN so as to specifythe logical unit. Also, the disk array apparatus 10 recognizes aphysically-set storage area (will be referred to as “physical storagearea” hereinafter) of the hard disk drive 18, while such a logicaldevice LDEV (Logical Device) corresponding to a storage area which islogically set by using this storage area is used as a unit. For example,one, or more sets of parity groups in the RAID5 system may correspond toone logical device.

Management of Data and Storage Expiration

The disk array apparatus 10 is provided with a system capable of holdingdata under safe condition which has been stored in the hard disk drive18 as to a required term. To realize the above-described system, each ofthe disk array apparatus 10 manages such information as to necessarystorage expiration, first guarantee expiration, second guaranteeexpiration, and the like. The necessary storage expiration is anexpiration that data which has been stored in the storage area providedby the hard disk drive 18 is required to be held under safe condition.The first guarantee expiration corresponds such an expiration capable ofguaranteeing that a logical unit (first logical unit, first storagearea) stores therein data under normal condition. Also, the secondguarantee expiration corresponds to an expiration capable ofguaranteeing that another logical unit (second logical unit, secondstorage area) of another disk array apparatus 10 connected to the IPnetwork 60 stores therein data under normal condition. As the firstguarantee expiration and the second guarantee expiration, for instance,a life period of the hard disk drive 18 is used. Also, as the firstguarantee expiration and the second guarantee expiration, for example, alife period of the disk array apparatus 10 may be employed, whichmanages this logical unit.

As to the above-explained system, FIG. 4 shows various sorts offunctions employed in the disk array apparatus 10. In FIG. 4, a datamove managing unit 410 judges as to whether or not necessary storageexpiration of data which has been stored in the logical unit (firstlogical unit) is expired after the first guarantee expiration. Then, inthe case that the necessary storage expiration of the data which hasbeen stored in the logical unit (first logical unit) is expired afterthe first guarantee expiration, the data move managing unit 410transfers the data stored in the logical unit (first logical unit) viathe IP network 60 to the logical unit (second logical unit) having thesecond guarantee expiration after the first guarantee expiration.

As previously explained, since the data which has been stored in thelogical unit (first logical unit) is transferred to the logical unit(second logical unit) of another disk array apparatus 10 provided on theIP network 60, such a term can be extended during which the data storedin the logical unit (first logical unit) of the disk array apparatus 10of the data transfer source can be managed under safe condition. Also,in the case that necessary storage expiration is expired after the firstguarantee expiration of the logical unit (first logical unit), the datamove managing unit 410 may alternatively transfer the data which hasbeen stored in the logical unit (first logical unit) with respect tosuch a logical unit (second logical unit) having a second guaranteeexpiration subsequent to the above-explained necessary storageexpiration among the logical units (second logical units) of other diskarray apparatus 10. In this alternative case, the data move managingunit 410 may manage the data which has been stored in the logical unit(first logical unit) of the disk array apparatus 10 of the data transfersource under safe condition until the necessary storage expirationthereof.

In order to manage data under safe condition, even when the data istransferred under any of the above-described conditions, the data movemanaging unit 410 executes the transfer operation of the data which hasbeen stored in the logical unit (first logical unit) before theguarantee expiration (first guarantee expiration) of this logical unit(first logical unit) is expired.

The apparatus detecting unit 411 detects other disk array apparatus 10which are present on the IP network 60. This apparatus detectingoperation by the apparatus detecting unit 411 is carried out by way of,for example, either a broadcasting operation or a multi-castingoperation with respect to the IP network 60 so as to request a responsesent from an iSCSI device of a communication counter party.Alternatively, in the case that an iSNS (Internet Storage Name Server)may be used on the IP network 60, the apparatus detecting unit 44 mayperform the above-described apparatus detecting operation by executing adiscovery process in accordance with the iSNS.

The move destination logical unit managing unit 412 (second guaranteeexpiration managing unit) manages the move destination logical unitmanagement table 500. The move destination logical unit management table500 is stored in, for example, the memory 13, or the hard disk drive 18.

FIG. 5 shows an example of the above-explained move destination logicalunit management table 500. In this move destination logical unitmanagement table 500, an information has been registered. Thisinformation is related to the logical unit (second logical unit) ofanother disk array apparatus 10, which may constitute a move destinationcandidate of the data which has been stored in the logical unit (firstlogical unit). In this drawing, an apparatus ID which has been appliedto the disk array apparatus 10 constituting the move destinationcandidate is set to a column 531 of the apparatus ID. As this apparatusID, for example, an IP address; a combination between an IP address anda communication port ID provided on the side of another disk arrayapparatus 10 used to access a logical unit; an iSCSI-name (iSCSI name);and an apparatus number which has been applied to the disk arrayapparatus 10 when the manufacturer thereof ships this disk arrayapparatus 10 are employed. An LUN which has been applied to this logicalunit is set to a column 532 of LUN.

To a column 533 of an emulation type, an emulation type of this logicalunit is set. An emulation type implies information indicative of aspecification of a logical unit. For instance, a storage capacity, atrack size, a cylinder number, a maximum block number, and the like areset every emulation type to the emulation type column 533.

A storage capacity of this logical unit is set to a storage capacitycolumn 534 of the move destination logical unit management table 500. Toa format day/time column 535, day and time when this logical unit hasbeen formatted (initialized) are set. It should also be noted that whena logical unit has not yet been formatted, this format day/time column535 becomes blank.

A guarantee term (second guarantee term) is set to a guarantee termcolumn 536, which can guarantee that the logical unit (second logicalunit) stores thereinto data under normal condition. This guarantee termis determined based upon, for example, the life period of the hard diskdrive 18. In a case that the logical unit (second logical unit) isconstituted by employing storage areas of plural sets of the hard diskdrives 18, for instance, an averaged value of life periods of therespective hard disk drives 18 is set as this guarantee term. Guaranteeexpiration (second guarantee expiration) is set to a guaranteeexpiration column 537, which may guarantee that a logical unit storestherein data under normal condition. The guarantee expiration (secondguarantee expiration) may be calculated by adding the guarantee term(second guarantee term) set to the guarantee term column 536 to theday/time set to the format day/time. It should also be noted that whenformat day/time cannot be acquired from another disk array apparatus 10,a value is set to the guarantee expiration column 537, this value beingcalculated by adding the guarantee term (second guarantee term) set tothe guarantee term column 536 to a day/time when a second storage areaof another disk array apparatus 10 can be accessed.

The logical unit managing unit 413 (necessary storage expirationmanaging unit, first guarantee expiration managing unit) shown in FIG. 4manages a logical unit management table 600. FIG. 6 shows an example ofthe logical unit management table 600. The logical unit management table600 is stored in, for example, the memory 13, or the hard disk drive 18.Information related to a logical unit (first logical unit) has beenregistered in the logical unit management table 600. In this drawing, anLUN which has been applied to this logical unit (first logical unit) isset to an LUN column 631. An emulation type of this logical unit (firstlogical unit) is set to an emulation type column 632. A storage capacityof this logical unit (first logical unit) is set to a storage capacitycolumn 633.

A necessary storage term is set to a necessary storage term column 634,and this necessary storage term corresponds to a term that data storedin this logical unit (first logical unit) is required to be stored undersafe condition. A day/time when data was firstly written in this logicalunit (first logical unit) is set to a writing start day/time column 635.Necessary storage expiration is set to a necessary storage expirationcolumn 636, and this necessary storage expiration corresponds to such anexpiration that data stored in this logical unit (first logical unit) isrequired to be stored under safe condition. The necessary storageexpiration may be calculated by adding the value set to the necessarystorage term column 634 to the day/time set to the writing startday/time column 635.

Guarantee expiration (first guarantee expiration) is set to a guaranteeexpiration column 637, which corresponds to such a guarantee expirationthat this logical unit (first logical unit) can store data under normalcondition. The guarantee expiration (first guarantee expiration) of eachof the logical units may be calculated by adding the guarantee term(first guarantee term) to the day/time when this logical unit wasformatted. This first guarantee term implies a term that this logicalunit (first logical unit) can store the data under normal condition.

To a move required/not required column 638, a flag (0: move is required,1: move is not required) is set. This flag indicates as to whether ornot data which has been stored in a logical unit (first logical unit) isrequired to be moved to another logical unit (second logical unit) ofanother disk array apparatus 10. A value of this flag is determined bycomparing the necessary storage expiration set to the necessary storageexpiration column 636 of the logical unit management table 600 with theguarantee expiration (first guarantee expiration) set to the guaranteeexpiration column 637. In the case that the necessary storage expirationis expired after the guarantee expiration (first guarantee expiration),“1” corresponding to the flag for indicating that move is required isset to the move required/not required column 638. Also, in the case thatthe necessary storage expiration is expired before the guaranteeexpiration (first guarantee expiration), corresponding to the flag forindicating that move is not required is set to the move required/notrequired column 638. It should also be noted that as to the logical unit(first logical unit) which is not used, “2.” is set to the moverequired/not required column 638, “2” corresponding to a flag forindicating that this logical unit is an empty logical unit. When anotherdisk array apparatus 10 selects a logical unit of a move destination, asto such a logical unit that “2” has been set to the move required/notrequired column 638, this disk array apparatus 10 can judge that thislogical unit may be utilized as a logical unit of a move destination.

An apparatus ID of another disk array apparatus 10 having a selectedlogical unit is set to a move destination apparatus ID column 639. Asthis apparatus ID, for example, an IP address (otherwise, combinationbetween IP address and communication port ID provided on the side ofanother disk array apparatus 10 used to access to logical unit), aniSCSI-name (iSCSI name), and an apparatus number may be used. Thisapparatus number is applied to the disk array apparatus 10 when themanufacture thereof ships this disk array apparatus 10.

A logical unit number (LUN) of such a logical unit (second logical unit)which may constitute a candidate of a move destination among logicalunits (second logical unit) which have been registered in the movemanagement table 500 is set to a move destination logical unit column640. The logical unit management unit 413 selects such a logical unitwhich may constitute a candidate of a move destination from among thelogical units (second logical units) which have been registered in themove destination logical unit management table 500 as to each of thelogical units (first logical units) to the move required/not requiredcolumn 638 of which the move required “1” has been set, among thelogical units (first logical units) which have been registered in thelogical unit management table 600.

In this case, a fact as to whether or not a logical unit (second logicalunit) which has been registered in the move destination logical unitmanagement table 500 can constitute a candidate of a move destination isdetermined by judging as to whether or not guarantee expiration (secondguarantee expiration) of the logical unit which has been registered inthe move destination logical unit management table 500 is expired afterthe guarantee expiration (first guarantee expiration) of the logicalunit (first logical unit) of the logical unit management table 600. Inother words, the logical unit managing unit 413 selects a logical unit(second logical unit) as the candidate of the move destination, theguarantee expiration (second guarantee expiration) of which is expiredafter the guarantee expiration (first guarantee expiration), from theamong logical units (second logical units) which have been registered inthe move destination logical unit management table 500. It should alsobe noted that when the necessary storage expiration is expired after theguarantee expiration (second guarantee expiration), a data which hasbeen again thereafter stored in the logical unit (second logical unit)must be transferred to a logical unit having a guarantee expirationwhich is expired later than the second guarantee expiration at a timeinstant before the second guarantee expiration has elapsed. Aspreviously explained, as the condition for selecting the candidate ofthe move destination, among the logical units (second logical units)which have been registered in the move destination logical unitmanagement table 500, a logical unit (second logical unit) may beselected as the candidate of the move destination, the guaranteeexpiration (second guarantee expiration) of which is expired after thenecessary storage expiration set to the necessary storage expirationcolumn 636 of the logical unit management table 600.

A total number of logical unit (second logical unit) which is selectedby the logical unit managing unit 413 is not always a single logicalunit. That is to say, as to the logical unit (first logical unit) whichhas been registered in the logical unit management table 600, aplurality of logical units (second logical units) may be alternativelyselected from the move destination logical unit management table 500.Conversely, there is a certain possibility that none of such a logicalunit (second logical unit) which may constitute the candidate of themove destination is selected. In this case, both the move destinationapparatus ID column 639 and the move destination logical unit column 640become blank columns.

It should also be noted that the various sorts of functions shown inFIG. 4 have been executed by the disk array apparatus 10 in the abovedescriptions. Alternatively, these functions may be carried out by anapparatus (will be referred to as “managing server 30” hereinafter, seeFIG. 1) other than the disk array apparatus 10 connected to the IPnetwork 60. In this alternative case, the managing server 30 may alsostore thereinto both the move destination logical unit management table500 and the logical unit management table 600. The managing server 30transmits a message to the disk array apparatus 10 in the case thatnecessary storage expiration of a logical unit (first logical unit) of acertain disk array apparatus 10 is expired after the guaranteeexpiration (first guarantee expiration) of this logical unit (firstlogical unit), otherwise, in the case that the second guaranteeexpiration thereof is expired after the necessary storage expiration.This message instructs that data stored in this logical unit istransferred to another logical unit (second logical unit) of anotherdisk array apparatus 10 which owns a guarantee expiration (secondguarantee expiration) expired after the guarantee expiration (firstguarantee expiration), otherwise, the guarantee expiration (secondguarantee expiration) of which is expired after the necessary managementexpiration. The disk array which has received the message transfers thedata in accordance with the message. When the storage system 1 isarranged in such a manner that the above-described functions are carriedout by the managing server 30 as explained above, as to the processoperations executed by the managing server 30, the workload to beprocessed by the disk array apparatus 10 may be reduced.

Processing Operations of Storage System 1

Next, a description is made of process operations which are executed inthe storage system 1 according to this embodiment so as to realize theabove-explained data managing system.

FIG. 7A is a flow chart for explaining process operations related to anupdating operation of the move destination unit management table 500,which is carried out by the data move managing unit 410 of the diskarray apparatus 10. The apparatus detecting unit 411 of the disk arrayapparatus 10 (will also be referred to as “own apparatus 10′hereinafter) detects another disk array apparatus 10 (will also bereferred to as “another apparatus 10” hereinafter) which is connected tothe IP network 60 (step S711). It should be understood that a disk arrayapparatus 10 detected by the apparatus detecting unit 411 may be limitedto a predetermined range in order that such disk array apparatus 10 maynot be detected which need not be originally detected. To this end, forexample, while such an information for specifying iSCSI-name (iSCSIname) and an IP address of such a disk array apparatus 10 is stored intothe disk array apparatus 10, which may constitute a detection subject,the apparatus detecting unit 411 may alternatively detect only such adisk array apparatus 10 specified by this stored information.

When another apparatus 10 is detected by the apparatus detecting unit411, the data move managing unit 410 of the own apparatus 10 checks asto whether or not the detected another apparatus 10 corresponds to sucha disk array apparatus for managing the logical unit management table600 (step S712). In this step, this judgement may be carried out by, forexample, such a manner that the own apparatus 10 inquires as to whetheror not the logical unit management table 600 is managed by anotherapparatus 10. In this alternative case, for instance, the own apparatus10 may make this inquiry via the IP network 60 in accordance with theiSCSI protocol. Also, such a fact as to whether or not the detectedanother apparatus 10 corresponds to the disk array apparatus formanaging the logical unit management table 600 may be judged bypreviously storing such an information into the respective disk arrayapparatus 10 without using the iSCSI protocol, while this informationindicates as to whether or not another apparatus 10 manages the logicalunit management table 600. Furthermore, such a fact may also be judgedby checking as to whether or not a disk array apparatus 10 correspondsto such a disk array apparatus 10 manufactured by the same maker, orcorresponds to such a disk array apparatus 10 having the same modelnumber.

In a step S712, when the apparatus detecting unit 411 judges thatanother apparatus 10 corresponds to such a disk array apparatus formanaging the logical unit management table 600 (“YES”of step S712), thedata move managing unit 410 requests the detected another apparatus 10to transmit the logical unit management table 600. Then, anotherapparatus 10 transmits the logical unit management table 600 to the ownapparatus 10 in response to the above-explained response (steps S714 andS715). The own apparatus 10 receives the transmitted logical unitmanagement table 600 (step S716).

FIG. 7B is a flow chart for explaining a process operation which isexecuted in accordance with the iSCSI protocol while the own apparatus10 acquires the logical unit management table 600 itself, or acquires aportion of information registered in the logical unit management table600 from another apparatus 10. In such a case that the own apparatus 10requests either a portion of the information stored in the logical unitmanagement table 600 or the logical unit management table 600 itselffrom another apparatus 10, the own apparatus 10 firstly executes alog-in process operation with respect to another apparatus in accordancewith the log-in sequence of the iSCSI protocol (steps S751 to S754).

Next, a procedure at the SCSI protocol level is commenced. First, a READcommand of the SCSI protocol is transmitted from the own apparatus 10 toanother apparatus 10 (step S755). When the above-described READ commandis received by another apparatus 10 (step S756), another apparatus 10checks as to whether or not this READ command corresponds to such acommand for requesting either the logical unit management table 600itself or a portion of the information registered in the logical unitmanagement table 600 (step S757). This judgement is carried out bychecking information which has been set to a predetermined field of theREAD command. In this case, when the above-described READ command issuch a command which requires either the logical unit management table600 itself or a portion of the information registered in the logicalunit management table 600 (step S757: YES), another apparatus 10transmits either the logical unit management table 600 itself or aportion of the information registered in the logical unit managementtable 600 with respect to the own apparatus 10 (step S758). Then, theown apparatus 10 receives either the transmitted logical unit managementtable 600 or a portion of the information registered in the logical unitmanagement table 600 (step S759). In the above-explained step S757, whenthe above-described READ command is not such a command which requireseither the logical unit management table 600 itself or a portion of theinformation registered in the logical unit management table 600 (stepS757 NO), another apparatus 10 executes a process operation of the READcommand in accordance with the normal SCSI protocol (step S760).

In the step S712 of FIG. 7A, in the case that the apparatus detectingunit 411 judges that another apparatus 10 corresponds to such a diskarray apparatus which does not manage the logical unit management table600 (step S712: NO), the own apparatus 10 executes a log-in processoperation in accordance with the iSCSI protocol with respect to thedetected another apparatus 10 (steps S717 and S718). After the log-inprocess operation, the own apparatus 10 requests another apparatus 10 tosend information related to an iSCSI name, a size of a logical unit, andthe like (steps S719 and S720), and the own apparatus 10 receives suchan information transmitted from another apparatus 10 in response to therequest (steps S721 and S722).

In a step S723, the own apparatus 10 updates the move destinationlogical unit management table 500 based upon the logical unit managementtable 600 and the information as to the iSCSI name and the size of thelogical unit, which are received from the detected another apparatus 10.It should also be noted that another apparatus 10 corresponds to such adisk array apparatus 10 which is supplied from a maker different fromthe maker of this another apparatus 10, there are some possibilitiesthat information related to a format day/time, a guarantee term, andguarantee expiration cannot be acquired from another apparatus 10. Insuch a case, the own apparatus 10 predicts that, for instance, such aday/time is equal to guarantee expiration (second guarantee expiration)of a logical unit of another apparatus 10, while this day/time iscalculated by adding the life period of another apparatus 10 to such aday/time when the own apparatus 10 can access the logical unit ofanother apparatus 10. When the own apparatus 10 performs thisassumption, the own apparatus 10 notifies such a message that such anassumption has been carried out to the output apparatus 16 such as adisplay, and prompts a user, or the like to enter such a confirmation asto whether or not the data is moved to the input apparatus 15 whenmoving of this data is carried out. Only when the confirmation isentered, the own apparatus 10 transfers the data.

As previously described, in each of these disk array apparatus 10 whichare connected to the IP network 60, the content of the move destinationlogical unit management table 500 is updated. It should also be notedthat the updating operation of the move destination logical unitmanagement table 500 is properly carried out in real time, or atpre-scheduled timing.

FIG. 8 is a flow chart for explaining both a process operation forjudging as to whether or not data stored in the logical unit (firstlogical unit) of the disk array apparatus 10 is required to be moved,and another process operation for selecting such a logical unit (secondlogical unit) which constitutes a candidate of a move destination as tothe logical unit (first logical unit) storing the data the movement ofwhich has been judged to be required.

The data move managing unit 410 of the own apparatus 10 monitors thatdata which has been stored in each of the logical units (first logicalunits) employed in the own apparatus 10 is required to be moved toanother logical unit (second logical unit) of another apparatus 10 (stepS811). In this step S811, the data monitoring operation is properlycarried out in real time, or at prescheduled timing. The data movemanaging unit 410 checks as to whether or not necessary storageexpiration of data which has been stored in a storage area of a logicalunit (first logical unit) is expired after guarantee expiration (firstguarantee expiration) of this logical unit (first logical unit). Basedupon a checked result, the data move managing unit 410 determines as towhether or not movement as to the data stored in this logical unit(first logical unit) is required. The data move managing unit 410 sets“1” to the move required/not required column 637 of the logical unitmanagement table 600 of the logical unit (first logical unit) which hasbeen judged as “move being required”, and this flag indicates that thedata is required to be moved (step S812).

Next, as to such a logical unit (first logical unit) that the flag “1”indicative of “move being required” has been set to the moverequired/not required column 637 of the logical unit management table600, the data move managing unit 410 selects such a logical unit (secondlogical unit) which may constitute a candidate of a move destination(step S813). As previously explained, the selecting operation of thelogical unit (second logical unit) is carried out by comparing theguarantee expiration (first guarantee expiration) with the guaranteeexpiration (second guarantee expiration). The first guarantee expirationhas been set to the guarantee expiration column 637 of the logical unit(first logical unit) which has been judged as move being required.” Thesecond guarantee expiration has been set to the guarantee expirationcolumn 537 of the logical unit (second logical unit) which has beenregistered in the move destination logical unit management table 500. Aspreviously explained, the selecting operation of the logical unit(second logical unit) which may constitute the candidate of the movedestination may be carried out by comparing the necessary storageexpiration with the guarantee expiration (second guarantee expiration).The necessary storage expiration has been stored in the necessarystorage expiration column 636 of each of the logical units which havebeen judged as “move being required.” The second guarantee expirationhas been set to the guarantee expiration column 537 of each of thelogical units which have been registered in the move destination logicalunit management table 500.

Based upon the above-described comparing operation, the data movemanaging unit 410 selects such a logical unit that the second guaranteeexpiration is expired after the first guarantee expiration (otherwise,second guarantee expiration is expired after necessary storageexpiration) from the above-described move destination logical unitmanagement table 500. Then, the data move management unit 410 sets alogical unit number (LUN) of the selected logical unit (second logicalunit) to the move destination logical unit column 640 of the logicalunit management table 600. Also, the data move managing unit 410 sets anapparatus ID of another apparatus 10 which provides the selected logicalunit (second logical unit) to the move destination apparatus ID column639 of the logical unit management table 600.

In the above description, the disk array apparatus 10 automatically hasexecuted the judging operation as to whether or not the move of the datais required, and the selecting operation as to whether or not the movedestination of the logical unit is selected. Alternatively, both thejudging operation and the selecting operation may be manually set by auser, or the like by operating both the input apparatus 15 and theoutput apparatus 16 as user interfaces. When the setting operation ismanually carried out, the user, or the like may set values bymanipulating the input apparatus 15 to the move required/not requiredcolumn 638 of the logical unit management table 600, the movedestination apparatus ID column 639 thereof, and the move destinationlogical unit column 640 thereof, respectively, which are displayed onthe output apparatus 16 such as the display. It should also be notedthat for the sake of convenience as to the input operation by the user,or the like, the content of the move distance logical unit managementtable 500 may be displayed on the output apparatus 15. In this case, theuser, or the like may alternatively set the values to all of the moverequired/not required column 638, the move destination apparatus IDcolumn 639, and the move destination logical unit column 640, or maymanually set the value only to the move required/not required column638. Moreover the user may manually set the value only to the moverequired/not required column 638 and the move destination apparatus IDcolumn 639. Since such various setting methods are prepared, the settingoperation suitable for the operation mode of the user, or the like maybe set.

Now, in the case that a value has been set only to the move required/notrequired column 638, the data move managing unit 410 automatically setsboth the content of the move destination apparatus ID column 639 and thecontent of the move destination logical unit column 640. Also, in thecase that values have been set only to the move required/not requiredcolumn 638, and the move destination apparatus ID column 639, the datamove managing unit 410 automatically sets the logical unit of the diskarray apparatus 10 which has been set to the move destination apparatusID column 639 to the move destination logical unit column 640. It shouldalso be understood that a concrete process of a system capable ofautomatically selecting a candidate of a move destination is similar tothat of the above-explained case.

FIG. 9 is a flow chart for explaining a process operation related to amove of data, which is carried out in each of the disk array apparatus10 connected to the IP network 60. This data moving process operation isproperly carried out in either real time or at prescheduled timing. Thedata move managing unit 410 refers to the move required/not requiredcolumn 637 of the logical unit management table 600, and determines sucha logical unit (second logical unit) of another apparatus 10 as toanother logical unit (first logical unit) in which a flag “1” indicativeof “move being required” has been set. This second logical unitconstitutes a move destination of data which has been stored in thislogical unit (first logical unit).

When the data move managing unit 410 determines the second logical unitof another apparatus 10, the data move managing unit 411 firstly checksas to whether or not a logical unit (second logical unit) which mayconstitute a candidate of a move destination has been set to the movedestination logical unit of the logical unit management table 600 (stepS911). When the candidate of the logical unit (second logical unit)which may constitute the move destination has been set (step S911: YES),the data move managing unit 410 checks as to whether or not the logicalunit (second logical unit) which has been set to the move destinationlogical unit column 640 corresponds to a single logical unit. In thecase that only one logical unit (second logical unit) has been set tothe move destination logical unit column 640 (step S912: YES), the datamove managing unit 410 determines this single logical unit (secondlogical unit) as the logical unit of the move destination (step S913).

In the step S912, when a plurality of logical units (second logicalunits) have been set to the move destination logical unit column 640(step S912: NO), the data move managing unit 410 focuses on a logicalunit (second logical unit) of a move destination under predeterminedcondition (step S914). As this predetermined condition, for instance,the following conditions may be conceived: a condition as to whether ornot this guarantee expiration (second guarantee expiration) is expiredafter necessary storage expiration of a logical unit (first logicalunit) of a move source [note that this condition is applied to such acase that selecting condition of candidate corresponds to such acondition that guarantee expiration (second guarantee expiration) isexpired after guarantee expiration (first guarantee expiration)]; acondition as to whether or not this logical unit (second logical unit)has a sufficiently large remaining capacity capable of storing datawhich has been stored in the logical unit (first logical unit) of themove source (remaining capacity is acquired, for example, by makinginquiry from own apparatus 10 to another apparatus 10); and a conditionas to whether or not an emulation type of a logical unit set to the movedestination logical unit column 640 is identical to the emulation typeof the logical unit of the move source. In such a case that logicalunits (second logical units) which have been selected based upon theabove-described predetermined condition must be furthermore focused on asmaller number of such second logical units, the data move managing unit410 focuses on such a logical unit (second logical unit) of a movedestination by being selected from the plural logical units which havebeen selected under the predetermined condition for, for example, thelargest storage capacities, the latest expiration of guaranteeexpiration (second guarantee expiration).

It should also be noted that the number of logical units (second logicalunits) which are finally focused on may become single, or plural. In thecase that there are plural logical units which constitute candidates ofmove destinations, while the logical units which constitute thecandidates of the move destinations are informed to the output apparatus16, the user, or the like may designate the logical unit from the inputapparatus 15. As a consequence, such a logical unit which may constitutethe candidate of the move destination may be set in response to needs ofthe user, or the like.

On the other hand, in the step S911, in the case that the candidate ofthe logical unit (second logical unit) which may constitute the movedestination is not set to the move destination logical unit column 640of the logical unit management table 600 (step S911: NO), the data movemanaging unit 410 inquiries another apparatus 10 which has been detectedby the apparatus detecting unit 411 so as to acquire information relatedto the logical unit (second logical unit) of another apparatus 10 (stepsS915 to S918). When the data move managing unit 410 acquires theinformation related to the logical unit (second logical unit), the datamove managing unit 410 determines such a logical unit of a movedestination based upon the acquired information (step S919).

When this logical unit of the above destination is determined, the datamove managing unit 410 focuses on the logical unit (second logical unit)of the move destination based upon the following predeterminedconditions: a condition as to whether or not the guarantee expiration(second guarantee expiration) thereof is expired after the necessarystorage term of the logical unit (first logical unit) of the move source(otherwise, whether or not second guarantee expiration is expired afterfirst guarantee expiration of logical unit of move source); a conditionas to whether or not this second logical unit owns such an empty storagecapacity larger than, or equal to data size of data which has beenstored in the logical unit (first logical unit) of the move source; anda condition as to whether or not an emulation type of this secondlogical unit is identical to an emulation type of the logical unit(first logical unit). Similar to the above-described process operation,in the case that logical units (second logical units) which have beenselected based upon the above-described predetermined condition must befurthermore focused on a smaller number of such second logical units,the data move managing unit 410 focuses on such a logical unit (secondlogical unit) of a move destination by being selected from the plurallogical units which have been selected under the predetermined conditionbased upon the following condition for, for example, the largest storagecapacities, the latest expiration of the guarantee expiration (secondguarantee expiration).

It should also be noted that in the case that there are plural logicalunits which constitute candidates of move destinations, while bothinformation related to the respective logical units and the logicalunits which constitute the candidates of the move destinations areinformed to the output apparatus 16, the user, or the like may enterinformation for specifying the logical unit from the input apparatus 15.As a consequence, such a logical unit which may constitute the candidateof the move destination may be set in response to needs of the user, orthe like.

When the logical unit (second logical unit) of the move destination isdetermined in the above-explained manner, the data move managing unit410 transfers the data which has been stored in the logical unit (firstlogical unit) of the move source to such a logical unit (second logicalunit) which has been determined as the move destination (step S920). Tothe data which is transferred, an LUN of a logical unit (second logicalunit) which constitutes the transfer destination of this data isattached. Alternatively, in order that the user, or the like finallyconfirms the logical unit (second logical unit) of the move destinationbefore the data transfer operation is carried out, the logical unit(second logical unit) of the move destination may be informed to theoutput apparatus 16, so that the user, or the like is prompted to entersuch a confirmation as to whether or not the data transfer operation iscarried out. As a result, the user, or the like may finally make such aconfirmation, so that it is possible to avoid that the data istransferred irrespective of, for example, operation condition by theuser.

When the data move managing unit 410 employed in the disk arrayapparatus 10 having the logical unit (second logical unit) of the movedestination receives the transmitted data, this data move managing unit410 stores the received data into the relevant logical unit (secondlogical unit) having the LUN attached to this received data (step S921).The data move managing unit 410 of the disk array apparatus 10 of themove destination updates the content of the necessary storage termcolumn 634 contained in the logical unit management table 600 of thedisk array apparatus 10 of the move destination in order that thenecessary storage term of the moved data can be managed in a correctmanner (step S922). Concretely speaking, the data move managing unit 410employed in the disk array apparatus 10 having the logical unit (secondlogical unit) of the move destination sets such a value to the necessarystorage term column 634 of the logical unit management table 600 of themove destination. This set value is calculated by subtracting such aterm during which the above-explained moved data has been stored in thedisk array apparatus 10 of the move source from the content of thenecessary storage term of the logical unit management table 600 of themove source. In this case, the term during which the above-explainedmoved data has been stored in the disk array apparatus 10 of the movesource may be obtained as such a term defined from, for example, theday/time set to the writing start day/time column 635 of the logicalunit management table 600 up to day/time when the above-described datawas moved.

As previously described in detail, in accordance with the storage systemof the present invention, in the case that the necessary storageexpiration equal to the expiration which requires that the data storedin the storage area (first storage area) of the disk array apparatus 10is stored under the safe condition is ended after the first guaranteeexpiration of the relevant logical unit, the above-explained data storedin the first storage area is transferred in either the automatic mode orthe semi-automatic mode to another storage area (second storage area) ofanother disk array apparatus 10 having the second guarantee expirationexpired after the first guarantee expiration (otherwise, after necessarystorage expiration). As a result, with respect to such a term duringwhich the data is required to be managed under safe condition, the datacan be managed under safe condition.

Also, since the data transfer operation is carried out via the IPnetwork 60, the process operation can be quickly carried out, ascompared with such a case that the back-up data is stored in themagnetic tape, or the like. Also, since such an apparatus as a magnetictape apparatus for reading/writing data from a storage medium such as amagnetic tape is not separately employed, the management load and thecost can be decreased. Further, since the installation space forinstalling a magnetic tape apparatus, or the like is no longer required,space saving effects may be achieved.

Moreover, in accordance with the present invention, as explained above,in order to manage the data under safe condition as to the necessarystorage expiration, the second storage area of another disk arrayapparatus 10 is utilized. In other words, in accordance with the presentinvention, the storage areas provided by the respective disk apparatus10 which are connected to the storage system 1 can be effectively usedas the entire storage area of the storage system 1.

While the present invention has been described by exemplifying oneembodiment mode thereof, the descriptions of this embodiment areprovided in order to easily understand the present invention, but do notrestrict the present invention. Therefore, the present invention may bechanged and altered without departing from the gist of the presentinvention, and apparently, equivalents thereof are involved in thepresent invention.

1. A storage control apparatus for reading/writing data with respect toa storage device in response to a data input/output request transmittedfrom an information processing apparatus, which is used in a storagesystem arranged by containing a plurality of storage control apparatuswhich are connected via an IP (Internet Protocol) network to each otherunder communicatable condition, comprising: a necessary storageexpiration managing unit for storing thereinto a necessary storageexpiration equal to an expiration during which data is required to bestored under safe condition, said data being stored in a first storagearea corresponding to a storage area of said storage device to whichsaid storage control apparatus reads/writes the data; a first guaranteeexpiration managing unit for storing thereinto first guaranteeexpiration equal to an expiration during which said first storage areacan store the data under normal condition; a second guarantee expirationmanaging unit for storing thereinto second guarantee expiration equal toan expiration during which a second storage area can store the dataunder normal condition, said second storage area being equal to astorage area of said storage device to which another storage controlapparatus contained in said storage system reads/writes the data; and adata move managing unit operated in such a manner that when saidnecessary storage expiration of said first storage area is expired aftersaid first guarantee expiration of said first storage area, said datamove managing unit selects said second storage area having said secondguarantee expiration expired after said first guarantee expirationwithin said second storage area of said another storage controlapparatus, and transfers said data stored in said first storage area tosaid selected second storage area.
 2. A storage control apparatus asclaimed in claim 1 wherein: in the case that said necessary storageexpiration is expired after said first guarantee expiration of saidfirst storage area, said data move managing unit selects said secondstorage area having said second guarantee expiration expired after saidnecessary storage expiration within said second storage area of saidanother storage control apparatus, and transfers said data stored insaid first storage area to said selected second storage area.
 3. Astorage control apparatus as claimed in claim 1 wherein: said data movemanaging unit performs said data transfer operation before said firstguarantee expiration is expired.
 4. A storage control apparatus asclaimed in claim 1 wherein: said first storage expiration managing unitstores thereinto a necessary storage term corresponding to a term duringwhich the data stored in said first storage area is required to bestored under safe condition; and said necessary storage expirationmanaging unit stores thereinto day/time as said necessary storageexpiration, said day/time being calculated by adding said necessarystorage term to day/time when data was firstly written into said firststorage area.
 5. A storage control apparatus as claimed in claim 1wherein: said first guarantee expiration managing unit stores thereintoa first guarantee term corresponding to a term during which said firststorage area can store thereinto the data under normal condition; andsaid first guarantee expiration managing unit stores thereinto day/timeas said first guarantee expiration, said day/time being calculated byadding said first guarantee term to day/time when said first storagearea was formatted.
 6. A storage control apparatus as claimed in claim 1wherein: said second guarantee expiration managing unit stores thereintoa second guarantee term corresponding to a term during which said secondstorage area can store thereinto the data under normal condition; andsaid second guarantee expiration managing unit stores thereinto day/timeas said second guarantee expiration, said day/time being calculated byadding said second guarantee term to day/time when said second storagearea was formatted.
 7. A storage control apparatus as claimed in claim 1wherein: said second guarantee expiration managing unit stores thereintoa second guarantee term corresponding to a term during which said secondstorage area can store thereinto the data under normal condition; andsaid second guarantee expiration managing unit stores thereinto day/timeas said second guarantee expiration, said day/time being calculated byadding said second guarantee term to day/time when said storage controlapparatus could access said second storage area.
 8. A storage controlapparatus as claimed in claim 1 wherein: said first guarantee termcorresponds to a term during which it is guaranteed that said firststorage control apparatus is operated under normal condition; and saidsecond guarantee expiration corresponds to an expiration during which itis guaranteed that said second storage control apparatus is operatedunder normal condition.
 9. A storage control apparatus as claimed inclaim 1 wherein: said storage control apparatus is further comprised of:an apparatus detecting unit for detecting said another storage controlapparatus connected to said IP network; and said second storage areacorresponds to the storage area of said another storage controlapparatus detected by said apparatus detecting unit.
 10. A storagecontrol apparatus as claimed in claim 9 wherein: said apparatusdetecting unit detects said another storage control apparatus connectedto said IP network by a discovery process in accordance with an iSNS(Internet Storage Name Server) protocol.
 11. A storage control apparatusas claimed in claim 1 wherein: said storage control apparatus is furthercomprised of: a logical unit managing unit for providing said storagearea of said storage control apparatus, while a logical unit is used asa unit, and said logical unit is equal to a storage area which islogically set by employing a physical storage area provided by thestorage device; said necessary storage expiration managing unit storesthereinto said necessary storage expiration in correspondence with saidlogical unit; said first guarantee expiration managing unit storesthereinto said first guarantee expiration in correspondence with saidlogical unit; said second guarantee expiration managing unit storestherein said second guarantee expiration in correspondence with saidlogical unit; and in the case that said necessary storage expiration ofa first logical unit as said first storage area is expired after saidfirst guarantee expiration of said first logical unit, said data movemanaging unit selects a second logical unit having said second guaranteeexpiration expired after said first guarantee expiration from the secondlogical units as said second storage area of said another storagecontrol apparatus, and transfers said data stored in said first logicalunit to said selected second logical unit.
 12. A storage controlapparatus as claimed in claim 11 wherein: said data move managing unitstores thereinto a storage capacity as to each of said logical units;and in the case that said necessary guarantee expiration of said firstlogical unit is expired after said first guarantee expiration of saidfirst logical unit, said data move managing unit selects said secondlogical unit which owns said second guarantee term expired after saidfirst guarantee expiration, and also, has a storage capacity largerthan, or equal to said first logical unit from said second logicalunits, and said data move managing unit transfers said data stored inthe first logical unit to said selected second logical unit.
 13. Astorage control apparatus as claimed in claim 11 wherein: said data movemanaging unit manages a plurality of said second logical units; and inthe case that said necessary guarantee expiration of said first logicalunit is expired after said first guarantee expiration of said firstlogical unit, said data move managing unit selects said second logicalunit which owns said second guarantee term expired after said firstguarantee expiration, and also, has the largest storage capacity, andsaid data move managing unit transfers said data stored in the firstlogical unit to said selected second logical unit.
 14. A storage controlapparatus as claimed in claim 11 wherein: said data move managing unitstores thereinto both an emulation type of said first logical unit andan emulation type of said second logical unit; and in the case that saidnecessary storage expiration of said first storage area is expired aftersaid first guarantee expiration of said first storage area, said movemanaging unit transfers said data stored in the first storage area withrespect to said second logical unit whose emulation type is identical tothe emulation type of said first logical unit; and in the case that saidnecessary storage expiration of said first logical unit is expired aftersaid first guarantee expiration of said first logical unit, said movemanaging unit selects said second logical unit whose emulation type isidentical to the emulation type of said first logical unit, and whichowns said second guarantee expiration expired after said first guaranteeexpiration; and said data move managing unit transfers said data storedin said first logical unit to said selected second logical unit.
 15. Astorage control apparatus as claimed in claim 1 wherein: said storagecontrol apparatus is further comprised of: an output apparatus forshowing said second storage area which constitutes a move destination ofsaid data when said data is transferred by said data move managing unit;and an input apparatus for designating as to whether or not said datatransfer operation is executed; and said data move managing unitexecutes said data transfer operation in the case that an instructionfor instructing an execution of said data transfer operation is enteredto said input apparatus.
 16. A storage control apparatus as claimed inclaim 1 wherein: said storage control apparatus is further comprised of:an output apparatus for showing a plurality of second storage areaswhich constitute candidates of a move destination of said data; and aninput apparatus for accepting information for specifying said secondstorage area among said plurality of second storage areas represented onsaid output apparatus; and wherein: said data move managing unitexecutes said data transfer operation with respect to said secondstorage area specified by said accepted information.
 17. A storagecontrol apparatus as claimed in claim 1 wherein: said data transferoperation is carried out by said data move managing unit in accordancewith the iSCSI protocol.
 18. A storage control apparatus as claimed inclaim 17 wherein: said data move managing unit stores thereintoinformation for specifying said storage control apparatus which mayconstitute said another storage control apparatus, and executes saiddata transfer operation with respect to said second storage area of saidanother storage control apparatus specified based upon said informationstored thereinto.
 19. A storage system arranged by containing aplurality of storage control apparatus for reading/writing data withrespect to a storage device in response to a data input/output requesttransmitted from an information processing apparatus, which areconnected via an IP network to each other under communicatablecondition, wherein: said storage control apparatus is comprised of: anecessary storage expiration managing unit for storing thereinto anecessary storage expiration equal to an expiration during which data isrequired to be stored under safe condition, said data being stored in afirst storage area corresponding to a storage area of said storagedevice to which said first storage control apparatus reads/writes thedata; a first guarantee expiration managing unit for storing thereintofirst guarantee expiration equal to such an expiration during which saidfirst storage area can store the data under normal condition; a secondguarantee expiration managing unit for storing thereinto secondguarantee expiration equal to such an expiration during which a secondstorage area can store the data under normal condition, said secondstorage area being equal to a storage area of said storage device towhich said second storage control apparatus different from said firststorage apparatus reads/writes the data; and a data move managing unitoperated in such a manner that when said necessary storage expiration ofsaid first storage area is expired after said first guarantee expirationof said first storage area, said data move managing unit selects saidsecond storage area having said second guarantee expiration expiredafter said first guarantee expiration within said second storage area ofsaid another storage control apparatus, and transfers said data storedin said first storage area to said selected second storage area.
 20. Acontrol method for controlling a storage system arranged by containing aplurality of storage control apparatus for reading/writing data withrespect to a storage device in response to a data input/output requesttransmitted from an information processing apparatus, which areconnected via an IP network to each other under communicatablecondition, wherein: said storage control apparatus stores thereinto anecessary storage expiration equal to such an expiration during whichdata is required to be stored under safe condition, said data beingstored in a first storage area corresponding to a storage area of saidstorage device to which said storage control apparatus reads/writes thedata; stores thereinto first guarantee expiration equal to an expirationduring which said first storage area can store the data under normalcondition; and stores thereinto second guarantee expiration equal to anexpiration during which a second storage area can store the data undernormal condition, said second storage area being equal to a storage areaof said storage device to which another storage control apparatuscontained in said storage system reads/writes the data; and when saidnecessary storage expiration of said first storage area is expired aftersaid first guarantee expiration of said first storage area, said storagecontrol apparatus selects said second storage area having said secondguarantee expiration expired after said first guarantee expirationwithin said second storage area of said another storage controlapparatus, and transfers said data stored in said first storage area tosaid selected second storage area.